The present invention is directed to the field of controlled release rate fertilizers. More particularly, it is directed to the use of a sulfur/clay slurry as a forming agent for fertilizer components, a method of controlling the release of such fertilizer components, and a controlled release form of plant nutrient sulfate.
In the agricultural industry, it has long been accepted that it is preferable to apply fertilizer in a granular or pastille form. This has benefits both in terms of storage and in term of dissemination. It has proven difficult, with granulation techniques, however, to provide consistent particles of a uniform size which have specific release characteristics.
Looking firstly at granulation techniques, they can be achieved in various ways. For example, granular fertilizers can be produced through a chemical reaction in which heat is generated to produce granulation of a liquid form fertilizer, such as sulfuric and/or phosphoric acid or ammonia, into a solid form.
The incorporation of clay into fertilizers has long been used for a variety of reasons. For example, Canadian Patent No. 613,765 and U.S. Pat. No. 2,702,747 discuss the use of clay to coat hygroscopic materials such as ammonium sulfate to prevent coalescence of the fertilizer into a solid mass during storage.
U.S. Pat. No. 5,749,936 discloses a process for producing a dry granular fertilizer in which an aqueous slurry comprising clay and a dispersant is mixed with dry minerals or chemicals. The mixture is then fed to a granulator to produce the final product.
While this technology does prevent coalescence of hygroscopic materials and it does have some advantages over the coating technique of previous patents, it does not address another problem that is frequently encountered when using water soluble fertilizers, such as ammonium sulfate. During heavy rainfall or irrigation, water soluble fertilizers may be washed away before they have a chance to be absorbed by the plant. This results not only in a marked loss of efficiency but it also has serious environmental consequences.
The beneficial effects of blending a swelling clay material with liquid elemental sulfur and solidifying to create a controlled release plant nutrient sulfate fertilizer has been used for some time. The presence of the swelling clay in the solid sulfur particle accelerates the breakdown of the solid sulfur into the small particulate size distribution that favours subsequent microbiological conversion of the sulfur to plant nutrient sulfate. Cheap and available elemental sulfur can thus be used to control the rate of release of sulfur into the soil.
Control of the rate of release to the soil of many other forms of applied fertilizer materials has also been recognized to be agronomically important. Such control can minimize loss of water soluble fertilizers as a result of irrigation or heavy rainfall. It can greatly reduce the amount of applied fertilizer material that escapes into the aquasphere causing pollution of waterways. It can improve the uptake of fertilizer plant nutrient material by better timing the release to match plant needs. It can also help keep the fertilizer nutrients in the root growing zone of the soil and minimize sequestration by adsorption at deeper levels where it is unavailable to the plant. In the case of plant micronutrients, controlled release of high analysis fertilizer material prevents the development of toxic concentrations of these materials which are by definition required in very small quantities. Improving the spatial distribution of the micronutrient materials is also a benefit.
Sulfur has been previously used as a control release agent for other fertilizers. Sulfur coated urea (SCU) in various commercial forms is a generic example. There are, however, problems associated with using only elemental sulfur for such purposes. It has proven difficult to control and vary the rate of release. Elemental sulfur coatings may provide incomplete coverage or develop fractures with aging which allows ingress of water and rapid depletion of the carried fertilizer material. Also, a process that depends solely on the degrading of the sulfur by microbiological action to expose the carried fertilizer, is hard to control and is markedly dependent on soil temperature. Formulations that perform well in tropical or subtropical climates may perform poorly in temperate or cool soils. Adjustment of formulations and process conditions to meet these requirements using only elemental sulfur has not been well demonstrated.
Further attempts have been made to supplement sulfur as a control release agent by combining bentonite clays with sulfur to form a sulfur/clay matrix. An example of this composition is described in xe2x80x9cAnother Approach to S Forming; Sulfur September-October 1995xe2x80x9d and in xe2x80x9cGround, Degradable Sulfur Granules Suitable for Bulk Blending, Sulfur 99, 17-20 Oct. 1999. These articles describe sulfur granules produced in a granulation drum. The control of the granulation step is based on the recycle loop which is fed continuously with ammonium sulfate seed crystals. There is no discussion of the use of additional fertilizer material in this mixture.
Sulfur, both in its elemental form and as ammonium sulfate, are well recognized as important fertilizer components. However, there can be problems with its efficient delivery to the preferred site of action for the plant. For example, during times of heavy rain, ammonium sulfate may be washed away.
The present invention relates to how a controlled release property can be imparted into a fertilizer formulation by combining the fertilizer material or materials with a coating, carrier matrix or similar component comprising elemental sulfur in admixture with swelling clay(s). A variety of factors including i) the nature of the clay(s), ii) the amount of the clay(s), iii) the process of formulation with the carried fertilizer, and iv) the inclusion of other finely divided materials that can accelerate or decelerate breakdown, can all be adjusted in order to achieve a wide range of release rates.
The invention, in one aspect thereof, relates to the manufacture of a single fertilizer particle that combines a source of both immediately available sulfate and controlled release sulfate that is more resistant to loss by leaching. The invention synergistically combines ammonium sulfate and elemental sulfur components. By doing so, the release of the ammonium sulfate component is slowed down while the release of the elemental sulfur component is simultaneously accelerated by the use of swelling clays. Such a formulation obviates the need for physical blending of differently formulated particles and the undesirable abrasive interaction that can occur between the different components of such blends, often leading to dustiness in the blended product.
According to another aspect the generally spherical form of granulated fertilizer particles also helps to reduce the generation of fines due to abrasive inter particle interaction which, in turn, reduces the amount of such fines being rendered airborne as dust. The formulation can also be extended to include other essential fertilizer materials of both the macronutrient (N,P,K) and micronutrient kind (Fe, Cu, Zn, B, Mn, Mg etc.). The rate of release of these other fertilizers is also subject to the same control mechanism, leading to better distribution in the soil and more efficient and economic use of the fertilizer applied.
The granulation step may be performed by drum/falling curtain granulation, pan granulation, or any similar granulation process in which water is not a major component.
In accordance with another aspect of the invention, the control release rate formulation may be used in fertilizer slurries where the slurry is solidified into fertilizer pastilles on a pastillator machine. This provides an economical manufacture of pastilles with enhanced controlled rate of release features.
In accordance with an aspect of the invention, a fertilizer granule comprises:
i) an elemental sulfur and swelling clay matrix, and
ii) at least one additional fertilizer material incorporated into said matrix.
In accordance with another aspect of the invention, a process for the preparation of a controlled release fertilizer particle comprises the steps of:
a) preparing a liquefied mixture of sulfur and a swelling clay;
b) transferring said liquefied mixture to a granulator;
c) adding an additional fertilizer material to said granulator; and
d) collecting granules of a predetermined size.
In accordance with a further aspect of the invention, the use of a molten sulfur/clay slurry to prepare a matrix for the delivery of an additional fertilizer material.
In accordance another aspect of the invention, a sulfur-based slurry matrix for slowing down rate of release of an incorporated fertilizer component, said slurry comprises:
i) molten sulfur
ii) clay, and
iii) ammonium sulfate fines.
In accordance with a further aspect of the invention, the use of the slurry matrix in a pastillator to form fertilizer pastilles is also possible